Lower limb prostheses are generally attached to a residual limb by means of a liner and socket arrangement. The lower limb prosthesis is connected to a hollow socket, the shape of which corresponds to the external shape of the residual limb. A liner is placed over the residual limb and the residual limb together with the liner is inserted into the socket.
The residual limb is generally composed of bone, muscles, soft tissue and skin. During ambulation, the soft tissue experiences shear and compression forces at the interface with the liner and socket. The direction of the shear forces changes depending on whether the amputee is applying load to the prosthesis during stance phase or if the weight of the prosthesis is applying a load to the residual limb during swing phase. The alternating nature of these forces can lead to “pistoning” at the stump/socket interface. This effect is exaggerated if the socket is a poor fit or if the limb is heavy, which may be the case with some modern, highly functional prostheses. Whilst a liner made of resilient material moves with the residual limb to cushion and dampen these forces, over time, especially if left unchecked, these shear and compression forces combined with the movement of the residual limb inside the socket can cause discomfort and damage the skin and underlying tissues.
The force applied by the residual limb to the prosthesis can be harvested to expel air from any cavities which may exist between the residual limb and the socket if correct pathways are created to generate a vacuum. Such an arrangement is described in US-B2-8,308,815 to the present applicant, the content of which is incorporated herein by reference, which describes a vacuum-assisted liner system for a socket of a limb prosthesis, for securing the prosthesis to a residual body portion. A vacuum is created directly between the residual body portion and the socket to hold them together and minimise relative movement between them. The system includes a flexible liner made of an impermeable material, at least a distal part of the liner being porous to allow the transport of air and fluid directly away from the residual body portion to the outer surface of the liner. A fabric distribution layer is located over the liner and between the liner and the socket to allow transmission of such extracted air and fluid laterally over the liner to an evacuation port in the socket. Also disclosed is a limb apparatus suspension device incorporating the liner system, and a vacuum suspension device which secures a component such as a stump socket to a residual body portion by creating an evacuated space sealed by intimate contact directly between the socket and a boundary region of the liner.
A snug fit is required between the residual limb, the liner and the socket in order to adequately suspend the lower limb prosthesis from the residual limb, minimise friction associated with the movement of the residual limb inside the socket and to equalise contact pressures. As well as evenly distributing forces on the residual limb when weight is applied to the prosthesis via the socket whilst the lower limb is in contact with ground, the snug fit also contributes to the formation of a vacuum between the liner and the socket so that the lower limb prosthesis remains suspended from the residual limb during the swing phase of the gait cycle. The application of a low pressure to the amputee's residual limb can also aid in sweat management and improve circulation, both of which can have long term health benefits for the amputee. Hence, the presence of a low pressure between the socket and residual limb/liner is a desirable feature of such prostheses and it is an aim of the present invention to harvest the forces and “pistoning” action at the residual limb and provide a lower limb prosthesis incorporating a vacuum source as part of a system for providing a reduced pressure in the socket around the residual lower limb.
US-A1-2005/0143838 to Collier describes a prosthetic device for attachment to a residual limb that includes a pump that is adapted to draw a negative pressure within a socket forming member.
US-A1-2001/0016781 to Caspers describes an osmotic membrane and vacuum system for an artificial limb.
WO-A1-2014/109720 to Duger describes a foot with a vacuum unit activated by ankle motion.